The present invention relates to combinations, structures, devices, and methods for use in storing and applying heat softenable moisture curable materials such as adhesives, coatings or sealers.
Moisture curable adhesive materials (e.g., moisture curable urethane adhesives) are well known that are solid at room temperature, that can be heated to a flowable state for application, that after being applied between objects in their heated flowable state will adhere those objects together upon cooling, and that subsequent to solidifying will cure and build adhesive strength (i.e., adhesion to those objects and internal strength) by the absorption of atmospheric moisture. Such adhesive materials after being moisture cured can develop shear adhesion strength generally in the range of about 1000 pounds per square inch or about 690 newtons per square centimeter which is significantly greater than the range of shear adhesion strength of about 250 to 700 pounds per square inch or about 172 to 483 newtons per square centimeter that can be developed by conventional hot melt adhesives (i.e., hot melt adhesives are solid at room temperature, can be heated to a flowable state for application, after being applied between objects in their heated flowable state will adhere those objects together upon cooling, but have no means for developing significant further adhesive strength after cooling). While the adhesive strength of the moisture curable adhesive materials is not as high as that which can be developed using epoxy resins (i.e., epoxy resins can develop shear adhesion strengths in the range of about 2000 to 45000 pounds per square inch or 1379 to 3103 newtons per square centimeter), such moisture curable adhesive materials are more easily applied, require less clamping time before the material will solidify sufficiently to hold objects together, provide sufficient adhesive strength for use in many structural applications, and are less expensive than epoxy resins. Thus, there is significant commercial use of such moisture curable adhesive materials, particularly to join moisture vapor permeable materials (e.g., wood or plastic objects) together or to join one moisture vapor permeable material to another material that is not moisture vapor permeable (i.e., the moisture vapor permeable material or materials allow atmospheric moisture to enter and cure the adhesive material).
One problem with using moisture curable adhesive materials to join such objects is that they are typically applied using complex systems that are sealed against moisture, and the adhesive materials they apply must be heated to relatively high temperatures (e.g., 240 to 300 degrees Fahrenheit or 116 to 149 degrees Centigrade) before they will melt and can be applied. It takes a fairly long time (e.g., about 45 minutes) to initially bring the adhesive material in the system to the required application temperature, and maintaining the system at that temperature can normally only be justified if a fairly large amount of the adhesive material is to be applied over an extended period of time, such as to a series of objects moving along an assembly line. Thus, such moisture curable adhesive material application systems are impractical if only occasional applications of the adhesive material are required over an extended period of time.
The present invention provides a combination and method for storing and applying moisture curable materials (e.g., adhesives, coatings or sealers) that is inexpensive and practical for use even if only occasional applications of the moisture curable materials are required over an extended period of time.
This invention results from the recognition that moisture curable materials which, at about 140 to 230 degrees Fahrenheit or 60 to 110 degrees Centigrade, soften to a suitable flowable viscosity for application, can be stored in and applied from inexpensive container assemblies or syringes of polymeric materials that can withstand temperatures in that range and have sufficiently low surface energy that the moisture cured materials will not adhere well to them, even though, undesirably, those polymeric materials allow the passage of moisture vapor from the atmosphere. Even if moisture vapor transmission through the container assembly or syringe cures the material within it when the container assembly is exposed to the atmosphere, that cured material forms a bladder around uncured moisture curable material within the container assembly; and when the container assembly and material are heated into that range of about 140 to 230 degrees Fahrenheit or 60 to 110 degrees Centigrade that bladder will soften with the uncured material, will easily separate from the wall of the container assembly and collapse when pressure is applied to it because of the low surface energy of that wall, and will rupture under that pressure (or can be ruptured with an implement) so that the uncured material can be discharged from the container assembly.
The combination according to the present invention for use in storing and applying moisture curable materials comprises the container assembly or syringe including a tubular wall of moisture vapor transmissive polymeric material (e.g., material with a moisture vapor transmission (MVT) coefficient (cc-mil/100 square inchxe2x80x9424 hourxe2x80x94atm) of over 0.254 and up to at least 36), and a plunger or seal within the polymeric wall adjacent an inlet end of the wall that is adapted to move along the wall toward an outlet end of the wall in sealing engagement with an inner surface of the wall (e.g., a polypropylene or polyethylene syringe); and the moisture curable material within the chamber, which material is a solid at normal room temperature, will, when heated to a temperature in the range of about 140 to 230 degrees Fahrenheit or 60 to 110 degrees Centigrade, soften to a suitable flowable viscosity for application (e.g., a viscosity of less than 30,000 centipoise, preferably of less than 15,000 centipoise, and most preferably in the range of about 8,000 to 12,000 centipoise), and has little or no adhesion to the polymeric material in the tubular wall even when the material is moisture cured (e.g., the polymeric material in the tubular wall has a critical surface tension lower than about 35 dynes/centimeter). A removable layer or envelope of moisture impermeable material is provided entirely around the container assembly prior to its use. After (or possibly before) the container assembly is removed from the layer or envelope of moisture impermeable material it can be heated by various means to heat the moisture curable material within it to a suitable viscosity for application, after which various means can be used to drive the plunger along the wall toward its outlet end to discharge and apply the moisture curable material.
After the container assembly or syringe is removed from the layer or envelope of moisture impermeable material the moisture curable material within it will typically be useful for 3 to 4 days or more (i.e., that time may be extended if the moisture curable material is being used in a low humidity environment or if the container assembly or syringe is again sealed within the layer or envelope of moisture impermeable material between its uses to apply the moisture curable material). During the time that the container assembly or syringe is outside of the envelope and exposed to the atmosphere, atmospheric moisture vapor can pass through the walls of the container assembly or syringe, causing the moisture curable material to cure inwardly from its outer surface to form the bladder of the cured moisture curable material that will soften but will not melt upon heating. That bladder extends around a central core of uncured moisture curable material within the syringe that will still soften to a suitable viscosity for application when heated to a temperature in the range of about 140 to 230 degrees Fahrenheit or 60 to 110 degrees Centigrade. If the moisture curable material within the container assembly or syringe is thus heated and used within a short time after it is removed from the envelope of moisture impermeable material (e.g., within 1 to 10 hours) the thickness of that bladder will be negligible or so small that the bladder will easily rupture, flex, and easily separate from the wall of the container so that it will have no significant effect upon discharging the heated uncured moisture curable material from the container assembly or syringe. After a longer period of time (e.g., 12 to 96 hours) the bladder of moisture cured material can typically have become sufficiently thick (e.g., up to 0.06 inch or 0.625 mm thick) that it will have a significant effect upon discharging the heated uncured moisture curable material from the container assembly or syringe. That bladder, however, still may be ruptured by various means at the outlet end of the container assembly or syringe, and will be sufficiently flexible when heated and will be easily separable from the inner surface of the syringe (i.e., the moisture curable material even when cured has little or no adhesion to the polyolefin material forming the tubular wall) to afford movement of the plunger to flex or collapse the bladder and discharge the heat softened uncured moisture curable material from the syringe through that rupture in the bladder. With longer exposure to atmospheric moisture (e.g., over 4 days) the bladder of moisture cured material can have thickened sufficiently that it will be very difficult to rupture, however, the bladder becomes self sealing against further moisture penetration when it reaches a thickness of about xe2x85x9 inch (0.32 cm), thereby for a long time protecting a central core of the uncured moisture curable material that still can be heated and removed with significant difficulty such as the use of an awl or punch to rupture the bladder through the outlet end of the container assembly or syringe, after which the bladder when heated will still be soft, collapsible and separable from the tubular wall so that the uncured moisture curable material in the container assembly or syringe can be expelled.
The moisture curable material within the chamber can be a moisture curable urethane adhesive such as those having the designation TE-100, TE-200 or TS-230 xe2x80x9cJet Weldxe2x80x9d (T.M.) thermoset adhesive that are commercially available from Minnesota Mining and Manufacturing Company, St. Paul, Minn.
The tubular wall of moisture vapor transmissive polymeric material can be of a polyolefin material such as polyethylene or polypropylene which are readily available, relatively inexpensive, and have low surface energy or critical surface tension (i.e., it appears that the critical surface tension should be lower than about 35 dynes/centimeter which is the critical surface tension of ABS to which the moisture curable materials listed above will adhere quite strongly when moisture cured, but can be about 31 dynes/centimeter which is the critical surface tension of polyethylene, or about 29 dynes/centimeter which is the critical surface tension of polypropylene, to either of which those moisture curable materials have little adhesion when moisture cured). Polyethylene or polypropylene have relatively low Heat Deflection Temperatures under pressure which are reported in the Materials Selection chapter of Machine Design magazine""s xe2x80x9cBasics of Design Engineeringxe2x80x9d, June, 1994, the content whereof is hereby incorporated herein by reference. (e.g., under 64 pounds per square inch or 4.5 kilograms per square centimeter pressure the Heat Deflection Temperature (HDT) for medium density polyethylene is about 120 to 165 degrees Fahrenheit or 49 to 74 degrees Centigrade, the Heat Deflection Temperature for high density polyethylene is about 140 to 190 degrees Fahrenheit or 60 to 88 degrees Centigrade, and the Heat Deflection Temperature for unmodified polypropylene is about 200 to 250 degrees Fahrenheit or 93 to 121 degrees Centigrade). Such materials, however, can be suitable for use with the type of moisture curable material described above which softens to a suitable viscosity for application when heated to a temperature in the range of about 140 to 230 degrees Fahrenheit or 60 to 110 degrees Centigrade, and preferably in the range of about 180 to 190 degrees Fahrenheit or 82 to 88 degrees Centigrade. Syringes molded of these materials having various capacities (e.g., 32 cubic centimeters) and which have at the outlet ends of their walls a transverse end wall from the center of which projects a outlet nozzle are readily commercially available (e.g., from Plas-Pak Industries, Inc., Norwich, Conn.). Such a syringe filled with the moisture curable material that is sealed within the removable envelope of moisture impermeable material can be stored for a long period of time (e.g., over 6 months at 90 degrees Fahrenheit or 32 degrees Centigrade and 90 percent relative humidity).
The means for receiving the container assembly after it is removed from the envelope of moisture impermeable material and for heating the moisture curable material in it to a suitable viscosity for application can be an electrically heated cylindrical chamber adapted to closely receive the tubular wall of the container assembly. The container assembly can either be inserted into that chamber for a time sufficient to soften the moisture curable material and then removed from the chamber while the heated moisture curable material is applied, which facilitates manipulation of the container assembly or syringe during application of the moisture curable material; or the container assembly can remain in the heated chamber during application of the moisture curable material from an end portion of container assembly projecting from the chamber which insures that the moisture curable material will remain at the temperature needed for application over an extended period of time. If the container assembly remains in the heated chamber during application of the moisture curable material, that chamber can either be mounted at a fixed location, or can be moved with the container to a location at which the moisture curable material is to be applied. As an alternative to use of such a heated chamber, the container assembly can be heated by other means, such as by immersing the container assembly in boiling water, by the use of an oven, or otherwise.
The means adapted for engagement with the container assembly which can be activated to drive the plunger or seal along the tubular wall of the container toward its outlet end to discharge and apply the heated moisture curable material can be in the form of a projection of about the same length as the tubular wall that has an end in engagement with the plunger and projects from the inlet end of the tubular wall where it may be manually engaged at its opposite end to manually move the plunger and discharge the heated moisture curable material from the outlet end of the tubular wall. Alternatively, that means can be in the form of a commercially available applicator that has a frame adapted to engage the inlet end of the tubular wall, has a driver adapted for contact with the plunger, and has a ratchet mechanism between the frame and the driver assembly that is manually activateable to move the driver and thereby the plunger to discharge heated moisture curable material from the outlet end of the tubular wall. A suitable pneumatically or electrically operated applicator could also be used. Also, that applicator can either be portable or adapted to be mounted on a bench or the like.